The purpose of this study is to comprehensively characterize PMS using standardized medical, cognitive, and behavioral measures and to track the natural history of the syndrome using repeated longitudinal assessments. In addition, this study will be aiming to identify biomarkers using neuroimaging, including diffusion tensor imaging and identify genetic factors which contribute to diverse phenotypes in patients with PMS.

Phelan-McDermid syndrome (PMS) or 22q13 Deletion syndrome, caused by a loss of one copy of the SHANK3 gene, is characterized by global developmental delay/intellectual disability, motor skills deficits, delayed or absent speech, and autism spectrum disorder. The goal of this study is to understand more about the PMS phenotype and the biological pathways associated with ID and ASD in the disorder, and to establish the foundation for future clinical trials in PMS and in other ID/ASD-associated disorders that share signaling pathways with PMS.

Individuals with PMS will be asked to participate in this study if they are 18 months or older with pathogenic deletions or mutations of the SHANK3 gene at time of enrollment, as well as healthy controls. Both males and females will be asked to participate. Additionally, to be eligible for study participation, individuals' primary communicative language must be English. Parents and unaffected siblings may also be asked to consent to have blood drawn for analysis.

The study involves 3 on site visits over 2 years. Study visits involve a physical exam, medical history questions, blood work and neuropsychological assessments. A subset of participants between the ages of 2 and 11 years old will take part in the EEG portion of the study. Individuals who have a clinically indicated MRI will have an option to provide routine clinical scans for analysis.

Inclusion Criteria:

• Individuals older than 18 months of age with pathogenic deletions or mutations of the SHANK3 gene
• English speaking individuals

Exclusion Criteria:

• Has taken an investigational drug as part of another research study, within 30 days prior to study enrollment
• For subjects involved in imaging biomarker assessment: contraindications to 3T MRI scanning, such as metal implants/non-compatible medical devices or medical conditions, including vagus nerve stimulator
• For subjects involved in EEG/ ERP biomarker assessment: contraindications to EEG/ERP, such as uncooperative or destructive behaviors preventing lead placement or capture by ERP/VEP equipment. Under age 2 or over age 11 at the time of enrollment.
• Unwilling or unable to comply with study procedures and assessments

190 subjects with PMS will be enrolled across the 6 sites for this study